Inside a 20W charger
The short answer
A 20W USB-C charger filters and rectifies mains AC into high-voltage DC. It then switches that DC tens of thousands of times a second through a small transformer, which steps it down and isolates it from the mains. The output is rectified again and smoothed, and a protocol chip agrees 5 V or 9 V with your iPhone. Apple's 20W adapter does this with a custom silicon controller, and the 2023 revision merged three functions into one chip. 123
In 30 seconds
- Six stages: filter → rectify → switch → transform and isolate → rectify and smooth → negotiate.
- The transformer is what keeps mains voltage away from your phone. It is the heart of the safety design.
- Apple's 20W adapter is silicon-based: independent teardown found no gallium nitride (GaN) parts. 1
- Apple has made several revisions. Their measurements should never be mixed.
The six stages, explained
1. Input protection and filtering
Mains enters through the pins and meets a fuse first. In Apple's 20W adapter this is a Littelfuse 1.25 A, 250 V part. 31 Next comes an electromagnetic interference (EMI) filter: a common-mode choke and, in the 2023 revision, a colour-ring differential-mode inductor. 1 This filter keeps the charger's fast switching noise from travelling back into your home wiring.
2. Rectification and the bulk capacitor
A bridge rectifier (four diodes, marked R1M in the A2940) turns AC into pulsing DC. 1 Bulk electrolytic capacitors store energy between the peaks of the mains wave. At 230 V input the result is roughly 325 V DC, so these capacitors are rated at 400 V. The A2940 uses two 400 V 15 µF electrolytics, one from AiSHi and one from Chemi-Con. 1
3. The primary switch and controller
This is where the conversion happens. A power switch turns the high-voltage DC on and off at high frequency into the transformer. A controller decides how long each pulse lasts, so that output voltage stays steady whatever your iPhone draws. Most chargers in this class use a quasi-resonant (QR) flyback topology: simple, compact and efficient at 20W. 4
In Apple's adapters this stage is a custom Power Integrations chip: the ZN1461C in units torn down in 2021 and 2022, and the ZN1535C in the 2023 A2940. 231 Power Integrations' published InnoSwitch families combine the primary switch, the controller and an isolated feedback link (FluxLink) in one package. 4 The ZN parts are custom, and their internal details are not published.
4. The transformer and the isolation barrier
The transformer does two jobs. It steps the voltage down, and it provides galvanic isolation: no direct electrical path from the mains side to the USB-C side. Energy crosses as a magnetic field. The control signal crosses either through an optocoupler or, in Power Integrations' design, a safety-rated magnetic link. 4 In the A2940, ChargerLAB identifies the transformer as made by Salcomp. 1
A small Y capacitor bridges the barrier on purpose. It gives high-frequency noise a controlled path back to the primary side, which helps the charger pass EMI limits. It is a special safety-rated part. The A2940's is visible in teardown photos, but its rating was not reported. 1
5. Synchronous rectification and output smoothing
On the output side, the transformer's AC must be rectified again. Older chargers used a diode, which wastes energy as heat. Modern chargers use a synchronous rectifier: a low-resistance MOSFET switched in time with the transformer. Apple's 2022 and 2023 units use a Toshiba TPN1200APL (100 V, 9.8 mΩ). 31 A 2021 unit used a Diodes Incorporated part. 2 An output capacitor (a Nichicon 12 V 560 µF solid capacitor in the A2940) smooths what is left. 1 What remains after smoothing is the ripple, explained in ripple and power quality.
6. USB Power Delivery and the VBUS switch
Finally, a USB PD controller talks to your iPhone over the USB-C cable's configuration channel (CC) wire. It offers the voltages the charger supports, 5 V at 3 A and 9 V at 2.22 A on Apple's 20W 1, and the iPhone asks for one. A VBUS MOSFET connects the output to the port only once the handshake allows it. Apple uses an AOS AON7404G (20 V, 4.4 mΩ) in its 2022 and 2023 units 31, and an ON Semiconductor NVTFS4C10N in a 2021 unit. 2 The handshake is explained in how USB Power Delivery works.
How Apple's 20W design changed: the revisions
Apple has sold its 20W adapter since 2020 under several part numbers and model numbers. Independent teardowns show at least two internal architectures.
| Teardown date | Model number | Architecture | Main controller | USB PD chip | Synchronous rectifier | VBUS switch | Maker named | Source |
|---|---|---|---|---|---|---|---|---|
| Oct 2021 (iPhone 13 era) | not stated | Two-chip | PI custom ZN1461C | Cypress CYPD2134 | Diodes "T89" | ON NVTFS4C10N | not stated | 2 |
| Oct 2022 (iPhone 14 era) | not stated | Two-chip | PI custom ZN1461C | Infineon (ex-Cypress) CYPD2134 | Toshiba TPN1200APL | AOS AON7404G | Salcomp | 3 |
| Sep 2023 (iPhone 15 era) | A2940 | One-chip | PI custom ZN1535C, integrating primary switch, PWM, SR control and PD protocol | integrated | Toshiba TPN1200APL | AOS AON7404G | Salcomp | 1 |
What did not change: the outputs (5 V 3 A, 9 V 2.22 A), the protocols (PD 2.0 and the legacy DCP mode) and, by ChargerLAB's assessment, performance. 15 What changed is integration: one custom chip now does what two did.
Model numbers. Apple names A2305 as its 20W adapter in its fast-charge testing notes. 6 Independent testers report A2347 (an EU-plug unit, tested by techtest.org in 2020) and A2940 (the 2023 revision). 71 The current Apple India part number is MUVR3HN/A 8. Apple does not publish which A-number ships in India, and we have not found it.
Why revisions must not be mixed
A measurement belongs to the unit it was taken on. Efficiency, ripple and temperature depend on the controller, the transformer, the capacitors, the plug type and the test bench. Taking ripple from a 2023 A2940 test and size from a 2020 A2347 test, and calling the result "the Apple 20W", invents a product that was never tested. That is why every number below names its revision, its source and its conditions.
What independent tests measured
| Measure | Result | Unit tested | Conditions | Source |
|---|---|---|---|---|
| Conversion efficiency | 85.52–89.73% | A2940 | 220 V 50 Hz, range across loads | ChargerLAB, Sep 2023 5 |
| Conversion efficiency | 84.65–88.73% | A2940 | 110 V 60 Hz | 5 |
| Conversion efficiency | 83–88.8% | A2347 (EU) | load-dependent | techtest.org, Oct 2020 7 |
| No-load power | 0.021 W / 0.018 W | A2940 | 220 V / 110 V | 5 |
| Output ripple | 15–18 mVp-p (no load); up to 47.2 mVp-p (9 V 2.22 A) | A2940 | input voltage per figure not labelled | 5 |
| Case temperature after 1 h at 20 W | 42.1 °C front / 49.5 °C back | A2940 | 220 V, 25 °C room | 5 |
| Size and weight | 41.5 × 42.5 × 27 mm, 58.5 g; 0.42 W/cm³ | A2940 | — | 5 |
| Size and weight | 37 × 45 × 24 mm, 54.5 g | A2347 | EU plug | 7 |
The A2940 and A2347 dimensions differ partly because plug formats differ. A single unit was tested in each case, so these are indicative, not population averages.
Silicon, not GaN
ChargerLAB's teardown of the A2940 found "no GaN components". 1 This matters because "GaN" is often used as shorthand for a better charger. At 20W, a well-integrated silicon design meets its targets, and Apple's sits comfortably above the US and EU minimum average efficiency of about 85.5% for its rating. 910 Read more in silicon, GaN and SiC at 20W.
What we do not know
- The internal circuit of the custom ZN1461C and ZN1535C (not published).
- The varistor, thermistor and optocoupler arrangement, and the Y-capacitor rating, in any revision (not reported in text). 1
- Whether India-sold units differ internally from those torn down. No made-in-India teardown was found. Salcomp has manufactured chargers in Sriperumbudur since October 2020 11, but a link between that plant and a specific torn-down unit is not established.
- The A-number sold in India.
Myths
"Apple's 20W uses GaN." Independent teardown of the 2023 revision found no GaN parts. 1 "The new revision charges faster." ChargerLAB found performance essentially the same, with identical outputs. 5 "Made in China (or Vietnam) means fake." Apple adapters have been found from more than one country of manufacture 111. Country of origin alone does not prove anything. See is my charger genuine and check a BIS registration.
Frequently asked questions
What is the difference between Apple's A2305 and A2940? A2305 is the model Apple names for its 20W adapter. A2940 is the 2023 revision ChargerLAB tore down, with a single integrated controller replacing two chips. Both offer 5 V 3 A and 9 V 2.22 A. 61
Who makes Apple's 20W adapter? ChargerLAB's 2022 and 2023 teardowns name Salcomp as the manufacturer. 31
Does Apple's 20W adapter support PPS? No. ChargerLAB detected only USB PD 2.0 and the legacy DCP mode on the A2940. 1
Why is there a transformer in such a small charger? To step the voltage down and, above all, to isolate the USB-C side from the mains. High-frequency switching is what lets it be so small.
What does the Y capacitor do? It gives high-frequency switching noise a controlled path across the isolation barrier, which helps the charger meet interference limits. It is a safety-rated part.
Comparative caveats
Apple data here is quoted from independent teardowns with revision and date. Nothing on this page compares Apple's design with Fermi20. Any such comparison requires same-bench testing and legal review.